A cure for the deadly ebola virus, which has killed hundreds of people in West Africa, is "a very long way off", an expert has told Sky News.

David Evans, a professor of virology at Warwick University, said ebola is the latest disease to be transmitted "very efficiently" because of international travel.

More than 670 people in Sierra Leone, Liberia, Guinea and Nigeria have fallen victim to the viral illness, which has a fatality rate of up to 90%.

Those with ebola will often be overcome by a sudden onset of fever, as well as weakness, muscle pain and headaches.

The body is then gripped by vomiting, diarrhoea, rashes, kidney and liver problems and bleeding.

The time between infection and symptoms appearing is anything from two days to three weeks.

Ebola is spread through the direct contact with the blood, organs or other bodily fluids of those infected.

The liquid that bathes the eye and semen can transmit the disease, Prof Evans said.

Horseshoe bats are believed to be the natural host of the viral disease, he said.

"These bats transmit the virus between themselves, but periodically it then ends up in probably primates or other types of bushmeat which are then hunted by villagers and the virus is then transmitted from the sick animals to humans," he said.

Transmission has also been documented through the handling of chimpanzees, gorillas and porcupines.

One of the reasons for the disease's rapid spread is a tradition at burial ceremonies for mourners to have direct contact with the body of the deceased.

"Therefore barrier methods that prevent that direct contact, including things like washing of hands and things like that provide a reasonable level of protection," he said.

Healthcare workers treating patients are particularly at risk.

Public Health England said in a risk assessment published earlier this month said that the current outbreak could increase the risk for Britons working in humanitarian and healthcare delivery.

But the threat to tourists, visitors and expatriates is still considered "very low if elementary precautions are followed".

Prof Evans said there had been "periodic outbreaks" of ebola since the first recorded instances in 1976, but this is the deadliest so far.

There were two simultaneous outbreaks in Nzara, Sudan and Yambuku, a village in the Democratic Republic of Congo located near the Ebola River.

Data from the World Health Organisation shows the previous deadliest outbreak was the one in the DRC, when 280 out of 315 people infected died.

In the same country in 1995 another outbreak claimed 254 lives, with 315 patients infected.